/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements.  See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License.  You may obtain a copy of the License at
*
*     http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package javax.servlet.jsp;

import javax.el.ELContext;
import java.util.Enumeration;

/**
 * <p>
 * <code>JspContext</code> serves as the base class for the
 * PageContext class and abstracts all information that is not specific
 * to servlets.  This allows for Simple Tag Extensions to be used
 * outside of the context of a request/response Servlet.
 * <p>
 * The JspContext provides a number of facilities to the
 * page/component author and page implementor, including:
 * <ul>
 * <li>a single API to manage the various scoped namespaces
 * <li>a mechanism to obtain the JspWriter for output
 * <li>a mechanism to expose page directive attributes to the
 * scripting environment
 * </ul>
 * <p>
 * <p><B>Methods Intended for Container Generated Code</B>
 * <p>
 * The following methods enable the <B>management of nested</B> JspWriter
 * streams to implement Tag Extensions: <code>pushBody()</code> and
 * <code>popBody()</code>
 * <p>
 * <p><B>Methods Intended for JSP authors</B>
 * <p>
 * Some methods provide <B>uniform access</B> to the diverse objects
 * representing scopes.
 * The implementation must use the underlying machinery
 * corresponding to that scope, so information can be passed back and
 * forth between the underlying environment (e.g. Servlets) and JSP pages.
 * The methods are:
 * <code>setAttribute()</code>,  <code>getAttribute()</code>,
 * <code>findAttribute()</code>,  <code>removeAttribute()</code>,
 * <code>getAttributesScope()</code> and
 * <code>getAttributeNamesInScope()</code>.
 * <p>
 * <p>
 * The following methods provide <B>convenient access</B> to implicit objects:
 * <code>getOut()</code>
 * <p>
 * <p>
 * The following methods provide <B>programmatic access</b> to the
 * Expression Language evaluator:
 * <code>getExpressionEvaluator()</code>, <code>getVariableResolver()</code>
 *
 * @since 2.0
 */

public abstract class JspContext {

	/**
	 * Sole constructor. (For invocation by subclass constructors,
	 * typically implicit.)
	 */
	public JspContext() {
		// NOOP by default
	}

	/**
	 * Register the name and value specified with page scope semantics.
	 * If the value passed in is <code>null</code>, this has the same
	 * effect as calling
	 * <code>removeAttribute( name, PageContext.PAGE_SCOPE )</code>.
	 *
	 * @param name  the name of the attribute to set
	 * @param value the value to associate with the name, or null if the
	 *              attribute is to be removed from the page scope.
	 * @throws NullPointerException if the name is null
	 */

	public abstract void setAttribute(String name, Object value);

	/**
	 * Register the name and value specified with appropriate
	 * scope semantics.  If the value passed in is <code>null</code>,
	 * this has the same effect as calling
	 * <code>removeAttribute( name, scope )</code>.
	 *
	 * @param name  the name of the attribute to set
	 * @param value the object to associate with the name, or null if
	 *              the attribute is to be removed from the specified scope.
	 * @param scope the scope with which to associate the name/object
	 * @throws NullPointerException     if the name is null
	 * @throws IllegalArgumentException if the scope is invalid
	 * @throws IllegalStateException    if the scope is
	 *                                  PageContext.SESSION_SCOPE but the page that was requested
	 *                                  does not participate in a session or the session has been
	 *                                  invalidated.
	 */

	public abstract void setAttribute(String name, Object value, int scope);

	/**
	 * Returns the object associated with the name in the page scope or null
	 * if not found.
	 *
	 * @param name the name of the attribute to get
	 * @return the object associated with the name in the page scope
	 * or null if not found.
	 * @throws NullPointerException if the name is null
	 */

	public abstract Object getAttribute(String name);

	/**
	 * Return the object associated with the name in the specified
	 * scope or null if not found.
	 *
	 * @param name  the name of the attribute to set
	 * @param scope the scope with which to associate the name/object
	 * @return the object associated with the name in the specified
	 * scope or null if not found.
	 * @throws NullPointerException     if the name is null
	 * @throws IllegalArgumentException if the scope is invalid
	 * @throws IllegalStateException    if the scope is
	 *                                  PageContext.SESSION_SCOPE but the page that was requested
	 *                                  does not participate in a session or the session has been
	 *                                  invalidated.
	 */

	public abstract Object getAttribute(String name, int scope);

	/**
	 * Searches for the named attribute in page, request, session (if valid),
	 * and application scope(s) in order and returns the value associated or
	 * null.
	 *
	 * @param name the name of the attribute to search for
	 * @return the value associated or null
	 * @throws NullPointerException if the name is null
	 */

	public abstract Object findAttribute(String name);

	/**
	 * Remove the object reference associated with the given name
	 * from all scopes.  Does nothing if there is no such object.
	 *
	 * @param name The name of the object to remove.
	 * @throws NullPointerException if the name is null
	 */

	public abstract void removeAttribute(String name);

	/**
	 * Remove the object reference associated with the specified name
	 * in the given scope.  Does nothing if there is no such object.
	 *
	 * @param name  The name of the object to remove.
	 * @param scope The scope where to look.
	 * @throws IllegalArgumentException if the scope is invalid
	 * @throws IllegalStateException    if the scope is
	 *                                  PageContext.SESSION_SCOPE but the page that was requested
	 *                                  does not participate in a session or the session has been
	 *                                  invalidated.
	 * @throws NullPointerException     if the name is null
	 */

	public abstract void removeAttribute(String name, int scope);

	/**
	 * Get the scope where a given attribute is defined.
	 *
	 * @param name the name of the attribute to return the scope for
	 * @return the scope of the object associated with the name specified or 0
	 * @throws NullPointerException if the name is null
	 */

	public abstract int getAttributesScope(String name);

	/**
	 * Enumerate all the attributes in a given scope.
	 *
	 * @param scope the scope to enumerate all the attributes for
	 * @return an enumeration of names (java.lang.String) of all the
	 * attributes the specified scope
	 * @throws IllegalArgumentException if the scope is invalid
	 * @throws IllegalStateException    if the scope is
	 *                                  PageContext.SESSION_SCOPE but the page that was requested
	 *                                  does not participate in a session or the session has been
	 *                                  invalidated.
	 */

	public abstract Enumeration<String> getAttributeNamesInScope(int scope);

	/**
	 * The current value of the out object (a JspWriter).
	 *
	 * @return the current JspWriter stream being used for client response
	 */
	public abstract JspWriter getOut();

	/**
	 * Provides programmatic access to the ExpressionEvaluator.
	 * The JSP Container must return a valid instance of an
	 * ExpressionEvaluator that can parse EL expressions.
	 *
	 * @return A valid instance of an ExpressionEvaluator.
	 * @since 2.0
	 * @deprecated As of JSP 2.1, replaced by
	 * JspApplicationContext.getExpressionFactory()
	 */
	@SuppressWarnings("dep-ann") // TCK signature test fails with annotation
	public abstract javax.servlet.jsp.el.ExpressionEvaluator getExpressionEvaluator();

	public abstract ELContext getELContext();

	/**
	 * Returns an instance of a VariableResolver that provides access to the
	 * implicit objects specified in the JSP specification using this JspContext
	 * as the context object.
	 *
	 * @return A valid instance of a VariableResolver.
	 * @since 2.0
	 * @deprecated As of JSP 2.1,
	 * replaced by javax.el.ELContext.getELResolver()
	 * which can be obtained by
	 * jspContext.getELContext().getELResolver()
	 */
	@SuppressWarnings("dep-ann") // TCK signature test fails with annotation
	public abstract javax.servlet.jsp.el.VariableResolver getVariableResolver();

	/**
	 * Return a new JspWriter object that sends output to the
	 * provided Writer.  Saves the current "out" JspWriter,
	 * and updates the value of the "out" attribute in the
	 * page scope attribute namespace of the JspContext.
	 * <p>The returned JspWriter must implement all methods and
	 * behave as though it were unbuffered.  More specifically:
	 * <ul>
	 * <li>clear() must throw an IOException</li>
	 * <li>clearBuffer() does nothing</li>
	 * <li>getBufferSize() always returns 0</li>
	 * <li>getRemaining() always returns 0</li>
	 * </ul>
	 * </p>
	 *
	 * @param writer The Writer for the returned JspWriter to send
	 *               output to.
	 * @return a new JspWriter that writes to the given Writer.
	 * @since 2.0
	 */
	public JspWriter pushBody(java.io.Writer writer) {
		return null; // XXX to implement
	}

	/**
	 * Return the previous JspWriter "out" saved by the matching
	 * pushBody(), and update the value of the "out" attribute in
	 * the page scope attribute namespace of the JspContext.
	 *
	 * @return the saved JspWriter.
	 */
	public JspWriter popBody() {
		return null; // XXX to implement
	}
}
